This invention relates to a two-cycle motor having a fuel injection system for marine propulsion and more particularly to an improved arrangement for improving the efficiency and providing smooth low speed running for a two-cycle internal combustion engine.
As is well known, two-cycle internal combustion engines have a number of advantages. One of these advantages is the high output for a given specific weight because, unlike a four-cycle engine, the two-cycle engine fires each of its cylinders for each revolution of the crankshaft. With a four-cycle engine, the cylinders of the engine fire only once every second revolution of the crankshaft. However, the common form of two-cycle crankcase compression internal combustion engine employs a porting arrangement for transferring the intake charge from the crankcase where it is compressed to the combustion chamber where it is burned and then exhausted. In order to provide good power output, there is considerable overlap between the valve porting and this gives rise to poor running at low engine speeds. In many applications, a two-cycle is required to run at low speeds.
One of the prime applications for two-cycle engines is as the power unit of an outboard motor. As is well known, outboard motors are run at low engine speeds during conditions such as trolling. Under these running conditions, the two-cycle engine can provide poor fuel economy and uneven running because of the fact that a substantial portion of the intake charge may pass out the exhaust port without having been burned or a large portion of the exhaust gases may remain in the chamber and prevent the induction of sufficient fresh charges for good smooth running.
Devices have been proposed to try to improve the efficiency of two-cycle engines at low running speeds. Such devices operate upon the ignition system so as to cause misfiring of one or more cylinders under such low speed conditions. This misfiring will insure against poor fuel economy because the misfired cylinder has two cycles through which it can purge its combustion chamber and draw in a fresh charge before firing. However, when a multiple cylinder engine has less than all of its cylinders misfired, very rough running can occur because the firing impulses are no longer equal. That is, if one or more of the cylinders are misfired, the even firing impulses of the engine are upset and objectionable vibrations can occur.
It is, therefore, a principal object of this invention to provide an improved arrangement for insuring good fuel economy of a two-cycle engine during low speed running without causing irregular firing impulses.
It is a further object of this invention to provide an arrangement for insuring good low speed fuel economy without attendant irregular firing impulses.
Even if the engine fuel economy is improved by causing misfiring of the spark plugs, the arrangement for insuring the misfiring complicates the ignition circuitry and can give rise to the possibility of ignition system failures or malfunctions. In addition, this method cannot be employed in connection with two-cycle diesel engines that do not employ an ignition system.
It is, therefore, a still further object of this invention to provide an arrangement for insuring good fuel economy of a two-cycle engine at low speeds without the necessity of altering the ignition timing.
It is a yet further object of this invention to provide an improved arrangement for controlling the low speed fuel economy of a two-cycle engine that is independent of the ignition system and hence may be used with diesel engines.